Try This:
=IF(ISNUMBER(SEARCH("70001",A1)),"OK", "Not OK")
The formula doesnt seem to care if it is a number or text.
Change "70001" to whatever you want, Same with "OK" and "NOT OK"
A1 should change automatically as you copy down.
You can also find more in EXCEL Help - if you type "Contains" in the FIND Area of HELP